This invention relates to protective breathing apparatus of the type in which a user wears a face mask, sometimes referred to as a respiratory inlet covering, communicating with a source of air or other breathing fluid for use in toxic or oxygen deficient surroundings.
In the use of such breathing equipment, it is mandatory that pressure-demand apparatus be used where the atmosphere is highly toxic. Pressure-demand apparatus provides air on demand and in addition maintains a positive pressure within the face mask in relation to the ambient environment, during both inhalation and exhalation, thereby assuring that any leakage caused by poor facepiece fit or component failure will be outward from the mask to prevent inflow and possible inhalation of the atmosphere. However, a pressure demand regulator that will function as above will open to full flow position at all times that the users' face (or other means) does not close the man side of the mask to stop the flow and permit the build-up of positive pressure. If air is supplied to the regulator at such times it will deliver its maximum flow capacity, quickly depleting and wasting the air supply.
The evolution of user and buyer requirements as well as those of various regulatory agencies has seen an upward spiral of flow requirements such that modern regulators, in fully open position, can discharge enormous quantities of air as compared to the normal breathing requirements of a man. Over 500 liters per minute (17.6 cfm) is not unusual as a free flow regulator performance although the minimum approved quantity is 200 liters per minute. During donning and doffing or inadvertant removal of the mask this high flow will occur unless the air supply is off. It is difficult to don or doff and simultaneously turn the air on or off, and if the mask is forced off the wearers' face, for example during a fall, he may not be in a condition to immediately refit the mask or manually shut off the air supply. It is therefore desirable, and the object of this invention, to provide an automatic shut-off of the air supply in such situations where mask back pressure is lacking to prevent escape and rapid wasteful depletion of the limited air supply.
The details, operation, and benefits of the present invention will be described in detail with reference to the accompanying drawings.